Chapter 23: Southern Bluefin Tuna Fishery
H Patterson and M Dylewski
Note: SBT Southern bluefin tuna.
|Fishing mortality||Biomass||Fishing mortality||Biomass|
|Southern bluefin tuna (Thunnus maccoyii)||Not subject to overfishing||Overfished||Not subject to overfishing||Not overfished||The most recent (2020) estimate of total reproductive output is 20% of initial level. The global TAC, set in line with the management procedure, should allow rebuilding within the prescribed time frame.|
|NER are likely to be positive in an environment of low latency and positive lease prices for quota in a fishery managed with ITQs. Higher stock levels in recent years are likely to improve NER. Further stock rebuilding will ensure that the fishery's overall economic performance will continue to improve.|
a Status is based on the global assessment of southern bluefin tuna and the default limit reference point from the Commonwealth Fisheries Harvest Strategy Policy (Department of Agriculture and Water Resources 2018).
Notes: ITQ Individual transferable quota. NER Net economic returns. TAC Total allowable catch.
Area fished, fishing methods and key species
The Southern Bluefin Tuna Fishery (SBTF) spans the Australian Fishing Zone. Southern bluefin tuna (Thunnus maccoyii) is targeted by fishing fleets from several nations, both on the high seas and within the Exclusive Economic Zones (EEZs) of Australia, New Zealand, Indonesia and South Africa. Young fish (1–4 years of age) move from the spawning ground in the north-east Indian Ocean into the Australian EEZ and southwards along the Western Australian coast (Figure 23.1).
Since 1992, most of the Australian catch has been taken by purse seine, targeting juvenile southern bluefin tuna (2–5 years of age) in the Great Australian Bight. This catch is transferred to aquaculture farming operations off the coast of Port Lincoln in South Australia, where the fish are grown to a larger size to achieve higher market prices. Australian domestic longliners operating along the east coast also catch southern bluefin tuna, and there is some recreational fishing for the species.
The Commonwealth Fisheries Harvest Strategy Policy (Department of Agriculture and Water Resources 2018) does not prescribe management arrangements for fisheries managed jointly under international arrangements, such as the SBTF, which is managed under the 1994 Convention for the Conservation of Southern Bluefin Tuna. In 2011, the Commission for the Conservation of Southern Bluefin Tuna (CCSBT) adopted a management procedure (the Bali Procedure) that is analogous to a harvest strategy.
In 2019, the CCSBT adopted a new management procedure (the Cape Town Procedure) that aims to rebuild the southern bluefin tuna stock to 30% of its initial unfished biomass by 2035, with 50% probability. This new management procedure will be used to set the global total allowable catch (TAC) from 2021. The global TAC is allocated to members and cooperating non-members, as agreed by the CCSBT under the 2011 CCSBT Resolution on the Allocation of the Global Total Allowable Catch. The Australian Fisheries Management Authority sets the TAC for the SBTF, with reference to Australia's CCSBT allocation, using individual transferable quota (ITQ).
The number of vessels in the purse-seine fishery has been fairly stable, ranging from 5 to 8 since the 1994–95 fishing season. Since 2011, most fishing has occurred in the east of the Bight, closer to Port Lincoln, resulting in shorter towing distances to bring the fish to aquaculture farms for growing before harvest.
The number of longline vessels fishing for southern bluefin tuna off the east coast of Australia has been more variable, ranging from 11 to 24 vessels during the past 10 years. Effort in the longline sector is largely dependent on available quota.
|Fishery statistics a||2018–19 fishing season||2019–20 fishing season|
|Purse seine Pelagic longline||6,284 b n/a||5,308 766 c||$34.51 million $8.9 million||6,125 d n/a||4,586 843 c||$31.75 million $9.52 million|
|Total fishery||6,284||6,074||$43.41 million||6,125||5,429||$41.27 million|
|Effort e||Purse seine: 1,366 search-hours; 166 shots||Purse seine: 1,248 search-hours; 146 shots|
|Fishing permits||82 SFR owners at start of the season||82 SFR owners at start of the season|
|Active vessels||Purse seine: 7
|Purse seine: 7
|Observer coverage f||Purse seine: 22 shots (14.3%)
Longline: 11.7% (of hooks) in ETBF; 12.8% (of hooks) in WTBF
|Purse seine: 14 shots (9.9%)
Longline: 9.7% (of hooks) in ETBF; 12.1% (of hooks) in WTBF
|Fishing methods||Purse seine, pelagic longline, minor line (troll and poling)|
|Primary landing ports||Port Lincoln (South Australia)|
|Management methods||Output controls: TAC, ITQs, area restrictions to control incidental catches in the longline fishery|
|Primary markets||International: Japan – fresh, frozen|
|Management plan||Southern Bluefin Tuna Fishery Management Plan 1995|
a Fishery statistics are provided by fishing season, unless otherwise indicated. Season is 1 December to 30 November. GVP data are nominal values by financial year. b Australia carried forward ~119 t of undercatch to the 2018–19 TAC. A portion of the TAC (250 t) was set aside to cover recreational fishing mortality. c Includes some minor-line catch. d Australia carried forward ~40 t of overcatch to the 2019–20 TAC. The TAC set by the Australian Fisheries Management Authority Commission was 6,165 t. A portion of the TAC (250 t) was set aside to cover recreational fishing mortality. e Effort only for where southern bluefin tuna was caught. f Longline observer coverage is provided by calendar year, and is based on hooks observed only by the electronic monitoring system.
Notes: ETBF Eastern Tuna and Billfish Fishery. GVP Gross value of production. ITQ Individual transferable quota. n/a Not applicable. SFR Statutory fishing right. TAC Total allowable catch. WTBF Western Tuna and Billfish Fishery.
Southern bluefin tuna (Thunnus maccoyii)
Line drawing: FAO
Southern bluefin tuna constitutes a single, highly migratory stock that spawns in the north-east Indian Ocean (off north-western Australia, south of Indonesia; Figure 23.1) and migrates throughout the temperate southern oceans.
Troll catches of southern bluefin tuna off the east coast of Australia were reported as early as the 1920s, but significant commercial fishing for southern bluefin tuna commenced in the early 1950s with the establishment of a pole-and-live-bait fishery off New South Wales, South Australia and, later (1970), Western Australia. Purse-seine gear overtook pole as the main fishing method, and catches peaked at 21,500 t in 1982. Australia's catch of southern bluefin tuna was relatively stable from 1989 to 2009, when the global TAC and Australia's TAC were reduced because of the poor state of the biological stock (Figure 23.2). However, the global TAC and catch have been slowly increasing since implementation of the management procedure in 2011 (Figure 23.2).
Recreational angling for southern bluefin tuna in Australia has been popular among game fishers for many years. A survey of recreational fishing for southern bluefin tuna estimated a catch of 270 t in 2018–19 (95% confidence interval [CI] 232–292 t) (Tracey et al. 2020). Based on these results, and other considerations, the Australian Government determined that 5% of Australia's CCSBT annual allocation will be set aside for recreational fishing mortality, starting in the 2020–21 fishing season.
The reported global catch of southern bluefin tuna has declined since the peak catches in the early 1960s, and has been fairly stable since the mid-2000s (Figure 23.3). The Australian catch and TAC were stable from 1990 to 2009 and were then reduced as part of a global reduction in catch. Since adoption of the management procedure in 2011, the global TAC has increased. In 2019, Australia overcaught its quota by 40 t, but adjusted the TAC in the 2019–20 season to account for this. Indonesia also overcaught its quota in 2019 by 183 t. In addition, Indonesia indicated that it had overcaught its quota in 2020. However, the final catch figures for 2020 were not available in time to be considered here and will be discussed in the 2022 Fishery status reports. Indonesia has agreed to a plan to repay the overcatch.
Note: TAC Total allowable catch.
Note: Total global catches exceeded reported global catches between 1995 and 2005; some scientists estimate that unreported catches surpassed 178,000 t during this period (Polacheck & Davies 2008).
The management procedure specifies that there should be a full quantitative stock assessment every 3 years. In 2020, a revised CCSBT operating model (the quantitative model that is used to assess the spawning biomass of southern bluefin tuna, based on a variety of data sources), using data up to and including 2019, was used to run various scenarios to determine the impact of fishing on the stock (CCSBT 2020; Hillary et al. 2020). The updated assessment incorporated the half-sibling pair data from a close-kin genetic study, as well as parent–offspring pair data (Bravington, Grewe & Davies 2014; Farley et al. 2020) and data derived from the gene-tagging program (Preece et al. 2020). Similar to 2017, the 2020 assessment used an estimate of total reproductive output (TRO) instead of biomass of fish 10 years and older, due to the inclusion of the close-kin data. TRO is the absolute abundance of successfully reproducing adults in the population.
The reference set of operating models (or base case) for the assessment indicated that TRO is at 20% of the initial or unfished level (80% CI 16–24%). The ratio of current fishing mortality to the level associated with maximum sustainable yield (FMSY) was 0.52 (80% CI 0.37–0.73).
Stock status determination
The current mean estimate for TRO of southern bluefin tuna is 20% of unfished levels. As a result, the stock is now classified as not overfished.
The current level of fishing mortality is below the level that would result in MSY. In addition, the global TAC is set based on outputs from the management procedure, which should result in a level of fishing mortality that facilitates rebuilding of the stock to the agreed level. Based on the information provided above, the southern bluefin tuna stock remains classified as not subject to overfishing.
Key economic trends
Most southern bluefin tuna caught in the SBTF (approximately 85% of total catch) are transferred to aquaculture farms near Port Lincoln to be grown out before final harvest. The remainder of catch is typically line caught from the east coast and sold direct to market. Australia's southern bluefin tuna industry is highly export oriented, with most of the catch exported to Japan. In recent years, the line-caught sector of the fishery has contributed an increasing proportion of gross value of production (GVP) for the fishery.
The southern bluefin tuna aquaculture industry is vertically integrated, so there is no publicly visible point-of-landing price available for fish transferred to the farms. Therefore, an estimated price is required to determine the GVP of that component of the fishery. To estimate these prices, export unit prices (post-grow-out) are used as the starting point from which estimates of the costs of growing out fish in farms and resource rents are deducted. Based on this approach, estimated prices for southern bluefin tuna landed from the fishery for the aquaculture sector have varied in the last decade between $6.24/kg in 2015–16 and $8.81/kg in 2012–13. The beach price received for sold-direct product has been relatively stable since 2013−14 at an average of $9.25/kg.
GVP has been relatively stable in the past 10 years, averaging about $40 million per year (Figure 23.4). Over the last decade, the sold-direct part of the fishery's GVP has grown significantly, and in 2019–20 contributed nearly a quarter of the fishery's GVP.
No current bioeconomic model is available for the fishery, so it is not known what stock levels will maximise the net economic returns (NER) from the fishery. There is also no economic survey to estimate current NER. However, stock levels in the fishery have been steadily increasing over the past decade. Higher stocks in general lower the cost of fishing and improve NER. Quota latency has been low over the decade to 2019–20, indicating that positive economic returns are being generated; quota lease prices have also remained positive, suggesting that positive returns are being generated.
Note: GVP Gross value of production. ‘Real’ indicates that value has been adjusted for inflation.
Performance against economic objective
Consistently low quota latency and positive quota lease prices, along with a rebuilding stock, suggest that management arrangements are effective and a larger proportion of potential NER are likely being generated. The fishery is managed with ITQs, which provide fishers the incentive to minimise costs and maximise revenue for a given level of catch, and allows quota to flow to the most efficient fishers in the fishery. The recent increase in the share of the catch taken in the line sector of the fishery is a good example of ITQs at work – allowing quota to flow to its highest-value use.
The SBTF has approval for export until 11 November 2022. Conditions placed on the export approval include increasing confidence in the estimates of purse-seine catches; that the management arrangements start accounting for all sources of mortality of southern bluefin tuna, including recreational and Indigenous catch; and that the management arrangements continue to support the recovery of the stock.
A level 1 ecological risk assessment (ecological risk assessment for effect of fishing) of 50 species across 3 ecological components was completed in 2020. This provides a hierarchical framework for a comprehensive assessment of the ecological risks arising from fishing. No high risks were identified for any components assessed in the southern bluefin tuna purse-seine subfishery from internal activities (Bulman, Sporcic & Fuller 2020).
In accordance with accreditation under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act) (see Chapter 1, 'Protected species interactions') the Australian Fisheries Management Authority publishes and reports quarterly on interactions with protected species on behalf of Commonwealth fishing operators to the Department of Agriculture, Water and the Environment (DAWE). No interactions with protected species were reported for the SBTF in 2020. Interactions with sharks and other protected species using longline gear are discussed in Chapters 21 and 24, respectively.
These reported interactions with protected species form part of the ongoing monitoring by DAWE of the performance of fisheries within their accreditation under the EPBC Act.
Bravington, MV, Grewe, PG & Davies, CR 2014, Fishery-independent estimate of spawning biomass of southern bluefin tuna through identification of close-kin using genetic markers, FRDC report 2007/034, CSIRO, Hobart.
Bulman, C, Sporcic, M & Fuller M 2020, Report for the Southern Bluefin Tuna Fishery: purse seine sub-fishery 2015–2019, report for the Australian Fisheries Management Authority, Canberra.
CCSBT 2020, Report of the twenty-fifth meeting of the Scientific Committee, online meeting, 31 August to 5 September 2020, Commission for the Conservation of Southern Bluefin Tuna, Canberra.
Department of Agriculture and Water Resources 2018, Commonwealth fisheries harvest strategy policy, Department of Agriculture and Water Resources, Canberra.
Farley, J, Eveson, P, Gunasekera, R, Grewe, P & Bravington, M 2020, Update on the SBT close-kin tissue sampling, processing and kin finding, paper CCSBT-ESC/2008/07, 25th meeting of the Scientific Committee of the Commission for the Conservation of Southern Bluefin Tuna, online meeting, 31 August to 5 September 2020.
Hillary, RM, Preece, AL, Davies, CR, Takahashi, N & Itoh, T 2020, The assessment of stock status in 2020, paper CCSBT-ESC/2008/12 Rev. 2, 25th meeting of the Scientific Committee of the Commission for the Conservation of Southern Bluefin Tuna, online meeting, 31 August to 5 September 2020.
Polacheck, T & Davies, C 2008, Consideration of implications of large unreported catches of southern bluefin tuna for assessments of tropical tunas, and the need for independent verification of catch and effort statistics, CSIRO Marine and Atmospheric research paper 23, CSIRO, Hobart.
Preece, A, Eveson, JP, Bradford, R, Clear, N, Aulich, J, Lansdell, M, Grewe, PM, Cooper, S & Hartog, J 2020, Report of the SBT gene-tagging program 2020, paper CCSBT-ESC/2008/06, 25th meeting of the Scientific Committee of the Commission for the Conservation of Southern Bluefin Tuna, online meeting, 31 August to 5 September 2020.
Tracey, SR, Lyle, JM, Stark, K, Gray, S, Moore, A, Twiname, S & Wotherspoon, S 2020, National survey of recreational fishing for southern bluefin tuna in Australia 2018–19, University of Tasmania, Hobart.